NIMBA-Stabilized BH3-THF

Chemfiles Volume 5 Article 9

Borane-THF has long been a reagent of tremendous importance to synthetic organic chemists, utilized in reduction and hydroboration-oxidation as well as other transformations.1,2 As part of our ongoing commitment to safety, Sigma-Aldrich now introduces our new amine-stabilized BH3-THF solution (650412), stabilized with 0.005 M N-isopropyl-N-methyl-tert-butylamine (NIMBA).3

While Sigma-Aldrich continues to provide 1.0 M BH3-THF stabilized with 0.005 M NaBH4 (176192), the new amine- stabilized solution has a practical advantage in that all pack sizes offered (100 mL, 800 mL, 8 L, 18 L, and bulk) meet Self- Accelerated Decomposition Temperature (SADT) thresholds required for safe shipment at room temperature, while demonstrating excellent reactivity and selectivity. In contrast, as a safety precaution for 1.0 M BH3-THF stabilized with 0.005 M NaBH4, Sigma-Aldrich currently ships pack sizes above 100 mL only under cooled conditions.

In a comparative study, the NIMBA-stabilized BH3-THF solution was demonstrated to perform at the same high level as NaBH4- stabilized reagent in reduction (Scheme 1) and hydroboration (Scheme 2) reactions.

Scheme 1

Scheme 2

In the asymmetric reduction of acetophenone with Me-CBS in combination with BH3-THF, the NIMBA-stabilized solution exhibited improved enantioselectivities over the NaBH4-stabilized reagent (Scheme 3).

Scheme 3

For applications where the stabilizer is to be removed by a method other than aqueous/acidic work-up, users may find BH3-THF stabilized with NIMBA preferable to use due to its low boiling point (127 °C, 760 mmHg)4 and, hence, its simplified removal by evaporation.

1.0 M BH3-THF, whether stabilized with NIMBA or with NaBH4, should be stored at 2–8 °C. Stability studies do not indicate significant degradation/impurities when stored at 2–8 °C for 6 months. However, when stored at room temperature, degradation varies with stabilizer and 1.0 M BH3-THF exhibits superior stability when NIMBA is used as a stabilizer versus either unstabilized or stabilized with NaBH4.3

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  1. Brown, H. C.; Zaidlewicz, M. Recent Developments; Organic Syntheses via Boranes Series, Volume 2; Aldrich Chemical Co., Inc.: Milwaukee, 2001.
  2. Zaidlewicz, M.; Brown, H. C. Encyclopedia of Reagents for Organic Synthesis; Paquette, L. A., Ed.; J. Wiley: New York, 1995; Vol. 1, p 638.
  3. Josyula, K. V. B.; Potyen, M; Gao, P.; Hewitt, C. Patent Application Pending.
  4. Josyula, K. V. B.; Potyen, M.; Schuck, M.; Thomas, R.; Lu, S.; Gao, P. Hewitt, C. Presented at ACS Great Lakes Regional Meeting, Peoria, IL, PR-176, 2004

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